CN103078245A - Dissipation soliton active mode-locking fiber laser - Google Patents

Abstract

The invention discloses a dissipation soliton active mode-locking fiber laser, and relates to the field of a laser. The laser comprises a strength modulator and a code pattern generator, which are mutually connected, wherein the code pattern generator inputs pulse sequence signals to the strength modulator; and the strength modulator is used for modulating under the driving of the pulse sequence signals. The dissipation soliton active mode-locking fiber laser provided by the invention inputs the pulse sequence signals to the strength modulator by using the code pattern generator, so as to modulate laser pulse. Furthermore, the high-energy mode-locking laser pulse output can be obtained, and the center wavelength of the output laser pulse can be moved within a large range; and the output laser pulse has flexible and adjustable pulse repeat frequency, and can accurately align an external clock.

Description

Dissipation orphan Active Mode-locked Fiber Laser

Technical field

The present invention relates to the laser technique field, particularly a kind of dissipation orphan Active Mode-locked Fiber Laser.

Background technology

Fiber-optical ultrashort pulse laser has the characteristics such as volume is little and simple in structure, operation material is flexible media, easy to use, in field extensive uses such as optical fiber communication, laser processing, medical apparatus and instruments.

Fig. 1 is a kind of existing typical optical fiber laser structure figure.As shown in Figure 1, wherein, Pump is pumping source, and WDM is wavelength division multiplexer, and EDF is Er-doped fiber, and PC is Polarization Controller, and PDI is the relevant isolator of polarization, and OC is optical coupler, and Output is output.

This laser utilization be nonlinear polarization rotation (NPE) effect, principle is to utilize some nonlinear effects (from phase-modulation, Cross-phase Modulation, effect of dispersion) in the optical fiber and the equivalent fast saturable absorber that is made of the relevant isolator of polarization, two optical fiber polarization controllers that periodic modulation is carried out in the initial light pulse in the chamber to obtain to stablize ultrashort light pulse and export.

For this fiber laser that is formed by full negative dispersion optical fiber, pulse is to form in dispersion with under the acting in conjunction of the nonlinear effect as representative from phase-modulation, the pulse deformation that causes from phase-modulation and dispersion is simultaneously cancelled each other, can so that pulse shape remains unchanged, realize the running of fundamental soliton (a stationary soliton) in transmission course thus.This laser can be made all optical fibre structure, therefore can use the overwhelming majority to be applicable to the locked mode mode of mode locked fiber laser.The output pulse of this soliton laser is the hyperbolic secant shape, and spectrum is also near the hyperbolic secant shape simultaneously.

The pulse energy of soliton laser is generally all about 0.1nJ, because it can make pulse have quite high peak power without the narrow pulsewidth characteristic that chirping characteristics causes.The words that continue lifting orphan energy can make the too fast increase of peak power of pulse, and then make the nonlinear phase shift in the chamber surpass the limit that pulse can bear, thereby cause the generation of wave splitting phenomenon.

The laser advantage of this structure be simple in structure, can self-starting and can realize all optical fibre structure, its shortcoming and defect is: 1, pulse energy is low, because the existence of full negative dispersion in the chamber, so that orphan's formation is to produce under the balance of non-linear and dispersion, too high pulse energy produces stronger non-linear meeting and makes orphan's pulsing separating phenomenon, and then stops the further lifting of pulse energy; 2, structure is relatively fixing, is not easy to realize the adjustment of pulse repetition frequency; 3, output wavelength is difficult for regulating.

Fig. 2 is a kind of existing Totally positive dispersion optical fiber laser structure figure.As shown in Figure 2, wherein, Pump is pumping source, and WDM is wavelength division multiplexer, and YDF is Yb dosed optical fiber, and C is coupler, and PC is Polarization Controller, and PDI is the relevant isolator of polarization.

This Totally positive dispersion cavity mode-locked laser, be characterized in that the optical fiber in the chamber all is normal dispersion, in this laser, can produce high-octane dissipation orphan, reason is that just warbling from the phase-modulation generation of pulse can make broadening in the optical fiber of high-octane pulse in positive dispersion in the chamber, and then reduced the peak power of pulse, weaken nonlinear effect, avoided the generation of pulse division.Utilize this laser structure can produce the pulse of 20nJ energy.The shaping of pulse is based on the spectral filtering mechanism of chirped pulse in the positive dispersion cavity.Because pulse has very large warbling, so outside the chamber, can with light grid compression pulse to the fs rank, can realize that the impulse chamber external compression is to 80fs.On time domain, limited gain bandwidth has embodied the spectral filtering effect, thereby along the component frequency excision pulse is narrowed the front and back of pulse, and the positive dispersion medium can make pulse stretching, thereby obtains the balance and stability operation of pulse; On frequency domain, the filter effect of gain bandwidth is the spectrum widening effect institute balance brought by self phase modulation.In fact, just do not realize the spectral filtering effect by finite gain-bandwidth in the Totally positive dispersion laser, the modulating action of saturated absorbing body has been realized filter effect equally in the chamber.Utilize this structure, in the chamber, add Birefringent Filter, can realize that output wavelength is adjustable.

The advantage of this laser is to produce high-octane pulse, and can make all optical fibre structure, and the output pulse has very large warbling, and is compressible outside the chamber.Its shortcoming is: 1, wavelength is difficult for regulating; 2, because laser is the form of passive mode locking, thus be difficult to regulate the repetition rate that chamber length changes pulse, and then be difficult to pulse and outside clock synchronous are got up; Although 3 its realized that wavelength is adjustable, partly be space structure by the laser cavity that adds filter, structure is dumb and need to aim at, and pulse repetition frequency is difficult for regulating.

Fig. 3 is a kind of existing active mode locking laser structure figure.As shown in Figure 3, wherein Pump is pumping source, and WDM is wavelength division multiplexer, and EDF is Yb dosed optical fiber, OC is optical coupler, and ISO is isolator, and DL is delay line, and PC is Polarization Controller, Output is output, and Modulator is intensity modulator, and RF signal is radio-frequency signal source.

In this active mode locking laser, EDF provides gain for laser, and Modulator introduces periodic amplitude modulation(PAM) realization active mode locking together as locked mode device and microwave source.In the chamber, add a PC, be used for regulating the polarisation of light attitude, guarantee best modulation efficiency.Only have as modulating frequency f _mWith the long strict coupling in chamber, i.e. f _mEqual longitudinal mode spacing integral multiple (f _M=N * c/nL, n are refractive index, and L is that the chamber is long, and N is integer) time satisfy the locked mode condition, the pulse in the active mode locking laser could be each obtains maximum transmitance during through modulator, thereby is constantly pressed narrow and form mode locking pulse.Because the mode-locked laser amplifier section adopts EDF usually, remainder adopts general single mode fiber, and near the light the 1550nm is in the transmission of optical fiber dispersion region, and luminous power is higher in the ring laser, (SPM) is very strong from phase-modulation, and pulse can become orphan's form in the chamber.Utilize this mode can obtain 10GHz tunable wave length mode-locked laser.

This active mode locking laser generally adopts the RF signal (being sine wave signal) of 10GHz or higher rate to modulate, and then produces the mode locking pulse of high repetition frequency.It is long that adjusting DL can change laser chamber, and then adjust the repetition rate of pulse.

The advantage of the laser of this structure is: 1, repetition rate is high and can control, thus can with extraneous clock synchronous; 2, pulse chirp is little, near transform limit, has reduced the dispersive broadening of pulse in transmission course; 3, the tuning range of output wavelength is large, almost can cover the gain spectral scope of gain fibre; 4, laser cavity structure is flexible, can conveniently consist of various structures and realize the locked mode running.Its shortcoming is, this active mode locking laser is generally operational in higher repetition rate, the high repetition frequency of pulse limits the application of laser aspect data acquisition (such as bio-imaging, Optical Sampling oscilloscope) of this structure, and in the constant situation of average power, high repetition frequency causes the energy of pulse very low.

Summary of the invention

The technical problem that (one) will solve

The technical problem to be solved in the present invention is: how a kind of dissipation orphan Active Mode-locked Fiber Laser is provided, thereby makes Output of laser possess high-energy mode locking pulse output, and pulse repetition frequency flexibly adjustable, centre wavelength can move on a large scale.

(2) technical scheme

For solving the problems of the technologies described above, the invention provides a kind of dissipation orphan Active Mode-locked Fiber Laser, it comprises: interconnected intensity modulator and pattern generator; Described pattern generator is to described intensity modulator input pulse sequence signal; Described intensity modulator is modulated laser pulse under described pulse sequence signal drives.

Preferably, described laser also comprises: wavelength division multiplexer, gain fibre and optical coupler; Described wavelength division multiplexer, gain fibre, optical coupler and intensity modulator are connected monomode fiber and are connected and composed in turn laser cavity: the output of described intensity modulator connects the input of described wavelength division multiplexer; The output of described wavelength division multiplexer connects the input of described gain fibre; The output of described gain fibre connects the input of described optical coupler; The output of described optical coupler connects the input of described intensity modulator.

Preferably, described gain fibre adopts Yb dosed optical fiber.

Preferably, described laser also comprises the polarizer, and the described polarizer is arranged between described optical coupler and the intensity modulator.

Preferably, described laser also comprises Polarization Controller, and described Polarization Controller is used for optimizing the polarization state in the described laser cavity.

Preferably, described Polarization Controller is arranged between described gain fibre and the described optical coupler.

Preferably, described laser also comprises spacer, and described spacer is used for guaranteeing that laser pulse is in the one-way transmission of described laser cavity.

Preferably, described spacer is arranged between described intensity modulator and the described wavelength division multiplexer.

Preferably, described laser also comprises pumping source, and described pumping source connects the input of described wavelength division multiplexer.

Preferably, the fixed transmittance rate of described intensity modulator is:

$T=(1-{\mathrm{\α}}_m)\frac{1+\sin \left(\mathrm{\π}\frac{V}{V_{\mathrm{\π}}}\right)}{2}$

Wherein, V is the instantaneous voltage of described pulse sequence signal, V _πBe the half-wave voltage of described intensity modulator, α _mInsertion Loss for described intensity modulator.

(3) beneficial effect

Dissipation orphan Active Mode-locked Fiber Laser of the present invention, by adopting pattern generator to intensity modulator input pulse sequence signal, and then laser pulse modulated, obtained high-energy mode-locked laser pulse output, output laser pulse centre wavelength can move on a large scale, and the output laser pulse pulse repetition frequency is adjustable flexibly, can accurately aim at external clock.

Description of drawings

Fig. 1 is a kind of existing typical optical fiber laser structure figure;

Fig. 2 is a kind of existing Totally positive dispersion optical fiber laser structure figure;

Fig. 3 is a kind of existing active mode locking laser structure figure;

Fig. 4 is the structural representation of the described dissipation orphan of embodiment of the invention Active Mode-locked Fiber Laser.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used for explanation the present invention, but are not used for limiting the scope of the invention.

Fig. 4 is the structural representation of the described dissipation orphan of embodiment of the invention Active Mode-locked Fiber Laser.As shown in Figure 4, described laser comprises: pumping source 100, wavelength division multiplexer 200, gain fibre 300, Polarization Controller 400, optical coupler 500, the polarizer 600, intensity modulator 700, pattern generator 800 and spacer 900.

Monomode fiber connects described pumping source 100, wavelength division multiplexer 200, gain fibre 300, Polarization Controller 400, optical coupler 500, the polarizer 600, intensity modulator 700 and spacer 900 successively, consists of laser cavity.Wherein, described gain fibre 300 long 1.5m, all the other monomode fibers are 3m altogether, and laser cavity always is about 4.5m, and corresponding fundamental frequency is 44.1MHz.

Described pumping source 100 connects the input of described wavelength division multiplexer 200, is used for the input pumping laser; The be of coupled connections input of described gain fibre 300 of the output of described wavelength division multiplexer 200; The output of described gain fibre 300 connects the input of described Polarization Controller 400, the described gain fibre 300 preferred Yb dosed optical fibers that adopt; The output of described Polarization Controller 400 connects the input of described optical coupler 500, and described Polarization Controller 400 is used for optimizing the polarization state in the described laser cavity; The output of described optical coupler 500 connects the input of the described polarizer 600; The output of the described polarizer 600 connects the first input end of described intensity modulator 700, and the described polarizer 600 is used for guaranteeing that described intensity modulator 700 is operated in correct polarization state; The output of described intensity modulator 700 connects the input of described spacer 900; The output of described spacer 900 also connects the input of described wavelength division multiplexer 200, and described spacer 900 is for the laser pulse one-way transmission that guarantees in the described laser cavity; Described pattern generator 800 connects the second input of described intensity modulator 700; The output of described optical coupler 500 is also as the final laser pulse of the output port of described laser output, and its output is than being 10: 90.Described Polarization Controller 400 and the position of spacer 900 in described laser cavity are not limited in foregoing description, and its position can proper transformation, for realizing that the present invention program is without impact.

Wherein, described pattern generator 800 is used for comprising 1 and 0 pulse sequence signal to described intensity modulator 700 inputs, described intensity modulator 700 under described pulse train drives to the laser pulse modulation that narrows.The data rate of described pattern generator 800 is f _m=10.77GHz, however in every m=244 symbol, only have one " 1 ", and all the other are 243 (they being m-1) individual " 0 ".So the actual repetition rate that drives the pulse train of described intensity modulator 700 is f _m/ m is identical with the fundamental frequency of described laser.Corresponding only have a pulse to exist in time in one week of circulation in described laser cavity, and therefore in the constant situation of average power, it is very high that the energy of pulse can reach.

In the present embodiment, the propagation of laser pulse in laser cavity can be described (general non-linear Schrodinger equation) with following equation:

$\frac{\∂A}{\∂t}+\frac{i}{2}({\mathrm{\β}}_2+\mathrm{ig}/2{\mathrm{\Ω}}_g^2)\frac{{\∂}^{2}A}{\∂t^2}=i(\mathrm{\γ}+\frac{i}{2}{\mathrm{\α}}_2){\left|A\right|}^{2}A+\frac{1}{2}(g-\mathrm{\α})A---\left(1\right)$

Wherein A represents the normalization of light pulse electric field and becomes slowly envelope; | A| ²Represent the instantaneous power of light pulse; α is the loss factor in the laser cavity; α ₂The two photon absorption that represents described gain fibre can be ignored in Practical Calculation; β ₂The 2nd order chromatic dispersion coefficient of expression optical fiber, γ represents non linear coefficient in the laser cavity; G is the saturation gain coefficient of optical fiber, Ω _gIt is the fiber gain bandwidth; I represents imaginary unit, i ²=-1.

For monomode fiber gain coefficient g=0, for described gain fibre, its saturation gain coefficient g _GainFormula below satisfying:

Wherein,

The energy of laser pulse, g ₀Be described gain fibre small signal gain coefficient, E _SatIt is the saturation energy of described gain fibre.

Laser pulse circulates a week in laser cavity, and the fixed transmittance rate that described intensity modulator 700 forms is:

$T=(1-{\mathrm{\α}}_m)\frac{1+\sin \left(\mathrm{\π}\frac{V}{V_{\mathrm{\π}}}\right)}{2}---\left(3\right)$

Wherein V is the instantaneous voltage of modulation signal (being described pulse sequence signal), V _πBe the half-wave voltage of described intensity modulator 700, α _mInsertion Loss for described intensity modulator 700.In general the instantaneous voltage of modulation signal has comprised voltage and the dc offset voltage of high-frequency microwave modulation signal, therefore:

V＝V _bias+V _mcosω _mt (4)

V _BiasBe the bias voltage on the described intensity modulator 700, effect is the working point of selecting described intensity modulator 700.V _mBe microwave modulation voltage, ω _m=2 π f _mRepresent the angular frequency of modulation signal, f _mIt is the frequency of modulation signal.

In the present embodiment, 300 pairs of laser pulses of described gain fibre amplify, and described intensity modulator 700 provides a fixed modulation window that laser pulse is narrowed, and monomode fiber carries out broadening to laser pulse.The frequency of the pulse sequence signal of the output by the described pattern generator 800 of accurate adjustment can obtain stable dissipation soliton pulse output, and spectrum has precipitous edge.

Laser pulse centre wavelength can represent with following formula along with modulating frequency changes:

Wherein, χ represents the total dispersion in the laser cavity; f _Rep=f _m/ m is laser output pulse repetition frequency, also is the actual pulse repetition rate of pattern generator 800; δ _λIt is the moving range of output laser pulse centre wavelength;

It is the variation of laser output repetition rate.Since larger positive dispersion in the laser cavity, the transmission speed corresponding to different frequency part of laser pulse.Therefore, the wavelength of laser just can change along with the speed difference of described pattern generator 800, and needn't be by changing the means of the long this complexity in chamber.

In the embodiment of the invention, when the pumping laser wavelength is 974.3nm, when power is 195mw, can obtain the mode locking pulse that pulsewidth is 10ps, single pulse energy is 1.58nJ in the laser cavity.Simultaneously, when the speed of regulating described pattern generator 800 changes from 10.767GHz to 10.773GHz, can realize the movement of laser pulse centre wavelength 1030nm-1080nm, corresponding realization output laser pulse repetition rate 44.13MHz-44.15MHz's is tuning.

The described dissipation orphan of embodiment of the invention Active Mode-locked Fiber Laser, by adopting pattern generator to intensity modulator input pulse sequence signal, and then laser pulse modulated, obtained high-energy mode-locked laser pulse output, output laser pulse centre wavelength can move on a large scale, and the output laser pulse pulse repetition frequency is adjustable flexibly, can accurately aim at external clock.

Above execution mode only is used for explanation the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; in the situation that does not break away from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.

Claims (10)

1. a dissipation orphan Active Mode-locked Fiber Laser is characterized in that, comprising: interconnected intensity modulator and pattern generator; Described pattern generator is to described intensity modulator input pulse sequence signal; Described intensity modulator is modulated laser pulse under described pulse sequence signal drives.

2. laser as claimed in claim 1 is characterized in that, described laser also comprises: wavelength division multiplexer, gain fibre and optical coupler; Described wavelength division multiplexer, gain fibre, optical coupler and intensity modulator are connected monomode fiber and are connected and composed in turn laser cavity: the output of described intensity modulator connects the input of described wavelength division multiplexer; The output of described wavelength division multiplexer connects the input of described gain fibre; The output of described gain fibre connects the input of described optical coupler; The output of described optical coupler connects the input of described intensity modulator.

3. laser as claimed in claim 2 is characterized in that, described gain fibre adopts Yb dosed optical fiber.

4. laser as claimed in claim 2 is characterized in that, described laser also comprises the polarizer, and the described polarizer is arranged between described optical coupler and the intensity modulator.

5. laser as claimed in claim 2 is characterized in that, described laser also comprises Polarization Controller, and described Polarization Controller is used for optimizing the polarization state in the described laser cavity.

6. laser as claimed in claim 5 is characterized in that, described Polarization Controller is arranged between described gain fibre and the described optical coupler.

7. laser as claimed in claim 2 is characterized in that, described laser also comprises spacer, and described spacer is used for guaranteeing that laser pulse is in the one-way transmission of described laser cavity.

8. laser as claimed in claim 7 is characterized in that, described spacer is arranged between described intensity modulator and the described wavelength division multiplexer.

9. laser as claimed in claim 2 is characterized in that, described laser also comprises pumping source, and described pumping source connects the input of described wavelength division multiplexer.

10. laser as claimed in claim 2 is characterized in that, the fixed transmittance rate of described intensity modulator is:

$T=(1-{\mathrm{\α}}_m)\frac{1+\sin \left(\mathrm{\π}\frac{V}{V_{\mathrm{\π}}}\right)}{2}$

Wherein, V is the instantaneous voltage of described pulse sequence signal, V _πBe the half-wave voltage of described intensity modulator, α _mInsertion Loss for described intensity modulator.

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